Excitation of alternating-current machines



- Feb. 22, 1927. 1,618,725

D. C. PRINCE EXGITATION OF ALTERNATING CURRENT MACHINES Filed May 2, 1925 lnVentgar David C. rince,

y M J,

His Attorney.

Patented Feb. 22, 1921.

UNITED s'rn'rss raiser @Fhl-QIE.

DAVID C. IPWO'E, OI SCHENECTADY, NEW YORK, ASSIGNGR T fl-ENERQL ELECTRIC GOHPAKY, A. GORPORATIGN 6F HEW YQBK.

EXCITATIGN OF ALTEBNATIIING-GURBEHT MACHINES.

Application filed his 2, 1935. Serial Ho. 27,8599.

the same generator capacity is capable of deliverin I over a short transmission line.

It has been determined that a 200,000 kilovolt-ampere generator capacity, for example, is capable oi delivering only about 120,000 kilowatts at 220,000 volts over a line 250 miles long. If some method could be devised "for changing the generator excitation rapidly enough to neutralize the eliect of armature reaction, such a generator capacity would be capable of delivering about 190,000 kilowatts over a line 250 miles long. Inaccordance with my invention, the time inter- My invention relatestothe excitation of alternating current machines, and has for'its principal object the provision of improved regulating means whereby the voltage of an 6 alternating current machine may be maintained substantially constant irrespective of variation in its load current.' A further object is the provision of an improved arrangement for stabilizing the operation of l0 ynchronous machines interconnected through long transmission lines or other highly reae tive circuits whereby the line may be operated closer to its maximum power limit.

It is well known that the terminal voltage I of a synchronous generator is dependent on its field excitation and internal voltage drops; that these voltage drops vary with change in the generator load current; and

' that, in order to maintain the terminal voltage of the generator constant, the generator field excitation must be "adjusted simultaneously and inaccordance with changes in the current generated. Man of the arrange ments proposed and utilized for regulating the excitation of synchronous machines in the past have involved the use of a regulator connected to the machine load circuit in a manner to vary the machine excitation in accordance with the load current, the regulalo tor being arranged either to control the me.-

I chine excitation directly or to control the voltage of the exciter from which the field current of the machine is supplied. In the o oration of these and similar arrangements,

c anges in machine excitation are not produced simultaneously with changes in machine load current but occur some time thereafter, anddifiiculty is encountered due to the duct that the synchronizing force exerted belo tween the synchronous machines is likely to be greatly weakened before the machine voltage has been restored toits normal value. This difliculty is especially pronounced in the case of long power transmission lines or 4 other-highly reactive circuits because varia-' tions in line voltage large enough to produce instability in the operation of synchronous apparatus interconnected with the system are L likely to occur with changes in load. For

. this reason the maximumpower that can be delivered over a lon alternating current transmission line wit a given impressed voltage is much lower than the power that citation is greatly reduced through the use 01 a regulating arrangement for producing a generator excitation component that is proportional in value to the machine load current and changes at substantially the same instant as this current. By means of this arrangement, the maximum power that can be sion line 250 miles long can he increased in the ratio of to over that transmitted with the usual regulating arrangement.

My invention will he better understood from the following description when con- .sidered in connection with the accompanying drawing and its scope will he pointed out in the appended claims.

Referring to the drawing, Fig. 1 shows the generator end of a power transmission system wherein my invention has been embodied; and Fig. 2 shows further details of a transmission system arranged to be operated in accordance with my invention.

Fig. 1 shows a. synchronous generator or alternator provided with an armature winding which is connected to a transmission line with a field winding 4 which is arranged to have one component voltage applied to it by the vexciting machine 5 and another component voltage applied to it by the parallelconnected rectifying or vapor electric dedevices 6, 7 and 8, which are shown as mercury rectifiers, are connected to the transmission line 1' through seriestransformers 9, l0 and 11 respectivel that-the midpoint of each of these 1:

to one terminal of the alternator field cirtransmitted with stability over a. transmits val between change in alternator load and ex- 1 through slip rings 2 and brushes 3 and vices 6, 7 and 8. It will be observed that ormers, is connected cuit through a. conductor 12; that the cathof transformer 11 and wit odes 13, 14 and 15 of the devices 6, 7 and 8 that reactor 17 and resistor 18 are connected to the operating circuits of the devices 6, 7 and 8- in shunt to the alternator field and 'exciter' armature windings.- While means shown as a re ulator comprising an operating coil 19 and a core 20 iased to its illustrated position by a spring 21 have been provided for controlling the excitation of the exciter field winding 22 in accordance with the .voltage of the line 1, it will be apparent that a regulator of any suitable gype may be utilize for this purpose. The

evice 6 is provided with anodes 23 and 24 which are connected to opposite terminals of the current transformer 9 and with starting switch 25 and batte 26; the device 7 is provided with anodes and 28 connected to opposite terminals of transformer 20 and with starti 31 and 32 connected to opposite terminals starting switch 33 and battery 34. An inductive shunt may be connected across the secondary leads of the transformers 9, 10 and 11 to minimize the energy 'losses produced in the resistance 18. The same result may be produced by an airgapjii the core structures of these transformers.

Assuming the chronous generator to be in operation an operation of the devices 6, 7 and 8 to have been initiated by means of starting switches 25, 29 and 33, I the major part of the alternator excitation is supplie from the exciter 5 so lon as the alternator load is light. As the a ternator load increases in magnitude, however, the com onent 01E excitation supplied throu h the evi'ces 6, 7 and 8 increases in r'nagnitu e.

The regulator then functions to control the .field current of the exciter 5 in a manner to complement the voltage impressed on the field circuit by the exciter thus maintaining the alternator voltage at its normal value.

The alternator excitation thus coin rises two components, one of which is supp 'ed from the exciter 5 and tends to decrease as the alternator load increases and to lag somewhat behind the changes in alternator load current and the other of which is supplied through the devices 6, 7 and 8 and changes in value almost simultaneously with the variation in alternator load current. While but one field winding 4 has bmn shown it y will be apparent that separate field circuits supplied with current from the exciter and rectifiers res ectively"may be used. The component 0? alternator excitation supplied through the devices 6, 7 and 8 not' only the a ternator load current but also varies to be connected t switch 29 and battery 30; and the device 8 is likewise provided with anodes that ensures-stable operation of the under heavy load conditions.

chine com rising field an and rectifying means connected in directly asthis current and is the "hm factor in maintaining stable operation at heavy loads for the reason that it substan-' tially neutralizes the effect ofarmature reaction. 7 Where the alternator load is sub- Fig. 2 shows a synchronous motor providject to suddenchanges in value, the efiect of nent. supplied throu h ed with an armature windingconnected tothe line 1 throu h slip rings 35 and brushes 36 and with a old winding 37 'arran be en plied with current through exc1ter4l' and evices 38, 39 and 40. The devices 6, 7 and 8 oi'Fig. 2 are shown as provided with exciting circuits which com rise resistors 44, 45 and 46 respectivelyv an are arranged roughleads 42, and 43' to a source of suitable potential. The devices 38, 39 and 40 are likewise shown as provided with exciting circuits which comprise resistors 47, 48vand 49respectively and are arranged to be connected to a suitable source through leads 50 and 51. The arrangement and purpose ofthe other details shown in Fig. 2 will be readily understood in view nous motor excited by component field currents which respfond substantially instantaneously to changes in load current, the synchronizin' force exerted between the alternator an motorvis maintained at a value system The embodiments of the invention illustrated and described herein have been sele'cted for the urpose of clearly setting forth the princip as involved. It will be ap- I I parent, however, that the invention is susceptible'of being modified to meet-the difier ent conditions encountered in its-use and 1 therefore aim to cover by the a pended claims all modifications within t etrue spirit and scope of my invention. A

What I claim as new and desire to secu e by Letters Patent of the United States, is:

1'. The combination of a chronous macuits, a po yphase transmission line connects ed to said armature circuit, an exciter connected to said field circuit for applying thereto a component voltage which varies'inversely as the load current of said machine arallel between said field circuit and the ifierent phases of said transmission line for applying to said field circuit a com nent vo tage armature cirwhich varies directly as sai load current and at substantially the same time. chan as at substantially the same instant as 'cuits, a transmission line connected to said armature circuit, an exciter connected to said field circuit, means for adjusting the excitation of said exciter in response to variation in the voltage of said line, and vapor electric means interconnecting said line and said field circuit for applying to said field circuit a component voltage which varies directly as the load current of said generator and at substantially the same time.

3. The combination of a synchronous machine comprising field and armature circuits, a transmission line connected to said ari'nature circuit, an exciter connected tosaid field circuit, means for adjusting the excitation of said exciter in response to variation in the voltage of said line, and rectifying means connected to said field circuit in series with said exciter and arranged to apply thereto a component voltage which varies directly as the load' current of said machine and at substantially the same time.

4. The combination of a synchronous machine comprising field and armature circults, atransmission hne connected to said armature circuit, rectifying means interconnecting said field circuit and said line for applying to said field circuit voltage which varies directly as the load current of said generator and at substantially the same time, and means comprising a reactor connected between the direct current terminals of said rectifying means for amplifying said field voltage upon sudden changes in the value of said load current.

In Witness whereof, I have hereunto set my hand this 1st day of May, 1925.

i DAVID C. PRINCE. 

